In contrast to the Supreme Court, which was established by Article III of the Constitution, the district courts were established by Congress. There is no constitutional requirement that there be any district courts at all. Indeed, after the ratification of the Constitution, some opponents of a strong federal judiciary urged that the federal court system be limited to the Supreme Court, which would hear appeals from state courts. This view did not prevail, however, and the first Congress created the district court system that is still in place today.

United States district judges

A judge of a United States District Court is officially titled a “United States District Judge”. Other federal judges, including circuit judges and Supreme Court justices, can also sit in a district court upon assignment by the chief judge of the circuit or by the Chief Justice of the United States. The number of judges in each District Court (and the structure of the judicial system generally) is set by Congress in the Judicial Code. The President appoints all life-tenured federal judges (subject to the advice and consent of the Senate), so the nominees often share at least some of his convictions. In states represented by a senator of the president's party, the senator (or the more senior of them if both senators are of the president's party) has substantial input into the nominating process, and through a tradition known as “senatorial courtesy,” can exercise an unofficial veto over a nominee unacceptable to the senator.

With the exception of the territorial courts (Guam, the Northern Mariana Islands, and the Virgin Islands), federal district judges are Article III judges appointed for life, and can be removed involuntarily only when they violate the standard of “good behavior.” The sole method of involuntary removal of a judge is through impeachment by the United States House of Representatives followed by a trial in the United States Senate and a conviction by a two-thirds vote. Otherwise, a judge, even if convicted of a felony criminal offense by a jury, is entitled to hold office until retirement or death. In the history of the United States, only twelve judges have been impeached by the House, and only seven have been removed following conviction in the Senate. (For a table that includes the twelve impeached judges, see Impeachment in the United States.)

A judge who has reached the age of 65 (or has become disabled) may retire or elect to go on “senior status” and keep working. Such “senior” judges are not counted in the quota of active judges for the district and do only whatever work they are assigned by the chief judge of the district, but they keep their offices (called “chambers”) and staff, and many of them work full-time. A federal judge is addressed in writing as “The Honorable John Doe” or “Hon. John Doe” and in speech as “Judge” or “Judge Doe” or, when presiding in court, “Your Honor”.

District judges usually concentrate on managing their court's overall caseload, supervising trials, and writing opinions in response to important motions like the motion for summary judgment. Since the 1960s, routine tasks like resolving discovery disputes can, in the district judge's discretion, be referred to magistrate judges. Magistrate judges can also be requested to prepare reports and recommendations on contested matters for the district judge's consideration or, with the consent of all parties, to assume complete jurisdiction over a case including conducting the trial.

Federal magistrate judges are not Article III judges with guaranteed lifetime employment. Rather, they are hired and supervised by district judges like any other court employee, and they can be fired at any time for any rational reason (for example, if Congress cuts the judiciary's budget). Occasionally a capable magistrate judge will be nominated by the President to become a district judge, but magistrate judge is just one of the possible “stepping stones” to such an appointment.

In 2008, there were 678 authorized district court judgeships.

Jurisdiction

Unlike some state courts, the power of federal courts to hear cases and controversies is strictly limited. Federal courts may not decide every case that happens to come before them. In order for a district court to entertain a lawsuit, Congress must first grant the court subject matter jurisdiction over the type of dispute in question. Though Congress may theoretically extend the federal courts' subject matter jurisdiction to the outer limits described in Article III of the Constitution, it has always chosen to give the courts a somewhat narrower power.

The district courts exercise original jurisdiction over—that is, they are empowered to conduct trials in—the following types of cases:

Civil actions arising under the Constitution, laws, and treaties of the United States;

Certain civil actions between citizens of different states;

Civil actions within the admiralty or maritime jurisdiction of the United States;

Criminal prosecutions brought by the United States;

Civil actions in which the United States is a party; and

Many other types of cases and controversies

For most of these cases, the jurisdiction of the federal district courts is concurrent with that of the state courts. In other words, a plaintiff can choose to bring these cases in either a federal district court or a state court. Congress has established a procedure whereby a party, typically the defendant, can "remove" a case from state court to federal court, provided that the federal court also has original jurisdiction over the matter. For certain matters, such as intellectual property disputes and prosecutions for federal crimes, the jurisdiction of the district courts is exclusive of that of the state courts.

In addition to their original jurisdiction, the district courts have appellate jurisdiction over a very limited class of judgments, orders, and decrees..

Attorneys

In order to represent a party in a case in a district court, a person must be an attorney at law and generally must be admitted to the bar of that particular court. The United States usually does not have a separate bar examination for federal practice (except with respect to patent practice before the United States Patent and Trademark Office). Admission to the bar of a district court is generally granted as a matter of course to any attorney who is admitted to practice law in the state where the district court sits. The attorney submits his application with a fee and takes the oath of admission. Local practice varies as to whether the oath is given in writing or in open court before a judge of the district.

Several district courts require attorneys seeking admission to their bars to take an additional bar examination on federal law, including the following: the Southern District of Ohio, the Northern and Southern Districts of Florida, and the District of Puerto Rico.

The Central District of California is the largest federal district by population, since it encompasses practically all of the Los Angeles metropolitan area, while the City of New York is divided between the Southern and Eastern Districts of New York, and many New York suburbs are covered by district courts in New Jersey and Connecticut.

The Southern District of New York is the largest federal district by number of judges, with 46.

Extinct district courts

Most extinct district courts have disappeared by being divided into smaller districts. The following courts were subdivided out of existence:

From 1801 to 1802, and again from 1802 to 1872, the state of North Carolina was subdivided into the United States District Courts for the Districts of Albemarle, Cape Fear, and Pamptico. These courts were extinguished when the state was reorganized into the United States District Courts for the Eastern and Western Districts of North Carolina.